Charge-transfer processes resulting from collisions of H ϩ ions with H 2 , D 2 , CO, and CO 2 molecules have been experimentally investigated in the energy range of 0.2-4.0 keV by using the initial growth-rate method. Theoretical analysis based on a molecular-orbital expansion method for H 2 and CO targets was also carried out. The observed cross sections are compared with previous experimental and theoretical data. The present results for H 2 are found to be in excellent accord with the recommended data by Barnett ͓Oak Ridge National Laboratory Report No. ORNL-6086 ͑1990͔͒, and hence, confirm the accuracy of the recommended data. But, at 0.2 keV, the present data for D 2 are found to be smaller than those for H 2 . For the CO molecule, the present data qualitatively agree well with most previous measurements, but show the stronger energy dependence, while the present theory shows a pronounced structure at around 0.25 keV and ties well with other low-energy measurements below 0.1 keV. For the CO 2 molecule, the present results are in excellent accord with other measurements above 1 keV, while they show some differences below this energy where our experimental result displays the stronger energy dependence. These data are useful for various applications.

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